Originally Posted by Sam Drucker

Sounds like your argument is really about bulk, not weight. My 15kg was in a standard roller carryon, which would fit in a standard baggage sizer at the gate. I've seen a lot of backpacks in my time that would clearly not fit in a gate bag sizer. So the question becomes "should stepped-up gate enforcement really be focused on volume?" Within reason, weight is not going to create issues with other passengers not having enough space for their carry-ons.